A variety of liquid electrolytes are known in the prior art. However, liquid electrolytes have inherent issues concerning safety, thermal runaway, low voltage, and poor cycle life.
Complex metal hydrides (NaAlH4, LiAlH4, LiBH4, etc.) have been extensively evaluated for their hydrogen storage properties. However, these materials do not currently meet the US DOE requirements for solid-state on-board vehicular hydrogen storage. However, the physical and chemical properties of complex metal hydrides could be utilized as components in other energy storage and conversion devices. It is known in the art that LiBH4 undergoes a structural phase change (occurring at ˜390K) from orthorhombic to hexagonal upon heating. The high temperature phase (hexagonal) has a conductivity of 10−3 Scm−1 while the low temperature phase (orthorhombic) has between 10−8 and 10−6 Scm−1. Additionally, the phase transition from orthorhombic to hexagonal results in a lowering of the activation energy required for conduction from 0.69 eV to 0.53 eV. It is further known that the introduction of inorganic salts, anions, and metal dopants can significantly enhance the mobility of the Li ion in the solid state. Stable cycling in an all solid-state lithium ion battery utilizing pure LiBH4 as a solid-state electrolyte with LiCoO2 and Li metal as the cathode and anode respectively as also known. The reported cell demonstrated a stable reversible capacity of ˜86 mAh/g after 30 cycles when operated at 120° C. with a Li3PO4 thin film (˜25 nm) on the LiCoO2 cathode to prevent the highly reducing LiBH4 from reacting with the metal oxide cathode at the electrolyte/cathode interface. On the anode side, recent work has demonstrated that the ionic conductor LiBH4—LiI (3:1 mole ratio) can be used as coating to chemically passivate a Li3.833Sn08330.833As0.166S4 solid electrolyte and making it compatible with a metallic Li electrode and suggests a path forward to solve incompatibility issues observed for other ionic conductors with metallic Li electrodes. The hydrogen storage properties of a series of complex metal hydride-carbonaceous nanocomposites synthesized by a solvent-assisted mixing method have been evaluated. During these studies it was determined that C60 was superior to other carbon nanomaterials in that it facilitated the reformation of the complex metal hydride as well as participated in the hydrogen storage process through the formation of C—H bonds, as set forth in Teprovich, J. A.; Knight, D. A.; Peters, B.; Zidan, R. J. Alloys Compd. 2013, 580, S364-S367 and Teprovich, J. A.; Knight, D. A.; Wellons, M. S.; Zidan, R. J. Alloys Compd. 2011, 509S, S562-S566, which are incorporated herein by reference. In the examination of the LiBH4:C60 system, solid state NMR techniques identified amorphous components of the materials as well as mobile species in the material. Utilizing Li NMR, the fraction of highly mobile lithium species in the nanocomposite was monitored. It was determined that the fraction of highly mobile Li+ in the LiBH4—C60 as-prepared (before, heating and annealing) material was similar to that found in bulk LiBH4. However, when the material was heated to 300° C. and annealed for 1 hour, the fraction of highly mobile species at room temperature was significantly enhanced. After this annealing step at 300° C., the Li spectrum at room temperature is narrower by a factor of 5 when compared to the bulk LiBH4 and as-prepared LiBH4—C60 samples. This is similar to the effect observed when LiBH4 is ball milled with lithium halides.